Sputtering, referring to vapor deposition of an ion-bombarded target metal to form a thin metal film on a substrate, is widely used in the electronics industry. Thin-film magnetic recording disks, for example, are advantageously formed by sputtering successive thin-film layers, including an outer magnetic thin film, on a suitable disk-like substrate. Thin-film sputtering may be used in preparing optical recording medium and in semiconductor fabrication, for producing metal conductive layers on a silicon substrate.
The usual sputtering system consists of a series of sputtering stations at which successive thin-film layers are deposited on a substrate, as the substrate passes through the stations in a continuous through-put operation. Each station typically includes a target which is dimensioned to "cover" one or more substrates, as these are moved on a pallet below the target device. For example, in the usual commercial sputtering system used in forming thin-film magnetic recording media, a pair of disk-like substrates, carried in a side-by-side arrangement on a pallet, is moved through a succession of sputtering stations, in a front-to-back direction, to produce one or more underlayers, an outer magnetic thin film, and a protective coating. The overall method provides efficient, high through-put production of multi-layered thin-film media.
Despite these advantages, sputtering systems of the type mentioned above have not been entirely satisfactory, in that the sputtered layer may show significant crystal anisotropy and/or variations in layer thickness. Both types of surface nonuniformities lead to angular variations in magnetic signal properties, particularly at outer-track regions of a magnetic disk. As will be seen below, signal-amplitude variations of up to about 25%, as measured at an inner-diameter recording track, and up to about 40% as measured at an outer-diameter recording track, are typical in magnetic recording disks formed in sputtering systems of the type described above.
In theory, it should be possible to eliminate crystal anisotropy and variations in film thickness in a sputtering operation by rotating the substrates as they pass through each of the sputtering stations. However, it would be relatively difficult and expensive to adapt existing types of sputtering systems to provide simultaneous linear and rotational substrate movement through the various sputtering stations. An alternative approach which is compatible with the design of existing commercial sputtering machines would be to partition each sputtering target into a number of smaller target regions by placing multiple shields or baffles between the target and the region where deposition occurs. These baffles would act to prevent all but direct, high-angle deposition from the target onto the substrate. A number of baffle configurations, including a multi-web lattice or a plurality of relatively close-packed cylinders, would be suitable. Although this approach would result in a sputtered layer having an isotropic crystal structure and relatively uniform thickness, the time and amount of target material needed to form the layer would be relatively great, since a major portion of the sputtered material would be deposited on the walls of the baffles. Maintenance problems related to removing deposited material from the baffles regularly would be considerable, as well.